1. Field of the Invention
This invention relates to lubricant with perfluoropolyether and a magnetic recording medium having such a lubricant.
2. Background
There has been developed a magnetic recording medium of the thin metal layer type, in which a magnetic layer is formed on a non-magnetic base film by means of, for example, evaporating ferromagnetic metal material. In such a medium, the surface of magnetic layer is so smooth that substantial contacting area may become large against transporting elements such as magnetic heads and guide rollers. Since the coefficient of friction also becomes large, it causes some problems such as a sticking phenomena inviting unstabilized running characteristics and poor durability.
The use of many kinds of lubricant has been considered to improve the problem. It has been tried to decrease the coefficient of friction by coating higher fatty acid and its ester on the surface of magnetic layer of magnetic recording medium.
As the lubricant for use in the magnetic recording medium, there are very severe requirements on its characteristics. Up to the present, no conventional lubricant has completely satisfied the requirements. The following describes the requirements for the lubricant for use in the magnetic recording medium.
[1] To have an excellent low temperature characteristic to secure a certain lubricant effect when using in very cold area; PA1 [2] To be able to coat as an extremely thin film without causing any problem due to the space between a magnetic head, but with a sufficient lubricant characteristics; and PA1 [3] To have a long life time maintaining its lubricant effect after the use for long hours. PA1 (A) Compound of perfluoropolyether having hydroxyl group at its end and long chain carboxylic acid (see, general formula [11]). PA1 (B) Compound of perfluoropolyether having hydroxyl group at its end and partially fluorined long chain carboxylic acid (see, general formula [12]). PA1 (C) Compound of perfluoropolyether having carboxyl group at its end and partially fluorined long chain alcohol (see, general formula [13]). PA1 (D) Compound of perfluoropolyether having hydroxyl group at its end and perfluoro carboxylic acid (see, general formula [14]). EQU R.sup.f1 --CH.sub.2 OCOR.sup.1 EQU R.sup.1 COOCH.sub.2 R.sup.f1 CH.sub.2 OCOR.sup.1 general formula [ 11]
The conventional higher fatty acid and its ester become frozen and solidified in low temperature condition such as below zero centigrade. Therefore, it loses the function as a lubricant and tends to have no durability after the use for long hours.
The practical characteristics such as running characteristic and durability have not been satisfied yet because of the lack of ability of lubricant in use in the field of magnetic recording medium.